This invention relates to a safety device for fan heaters to prevent accidents resulting from the lack of oxygen.
In the conventionally known device of this kind, the burned gas from the burner is led through the draft to a detector pipe having a cylindrical oxygen density cell by which the density of oxygen in the burned gas is directly detected to operate the safety valve. In this case, however, if the burned gas should flow in unstable condition through the detector pipe and the combustion be stopped leaving the burned gas in the cylindrical oxygen density cell (the atmosphere in the heater then has a small amount of oxygen), the heater would fail to be reignited.
To eliminate the above drawback, it is desired that the burned gas be made to flow stably through the cylindrical detector pipes.
The object of this invention is to provide a safety device satisfying the above requirement which comprises: a detector pipe into which the burned gas from the burner is led; a cylindrical oxygen density cell having electrodes on the inner and outer surfaces thereof, the oxygen density cell being built into the detector pipe; a warm wind circulating fan with which the outlet of the detector pipe is communicated; whereby the safety valve in the gas pipe is operated by the output from the oxygen density cell. The oxygen density cell is a sintered, oxygen ion conductive solid electrolyte, such as zirconia, of a cylindrical shape with porous electrodes such as platinum formed on the inner and outer surfaces thereof. When heated to a predetermined operating temperature, the oxygen density cell generates voltage of a magnitude according to the oxygen density difference between the outer and inner atmospheres contacting the outer and inner electrodes.